1. Field of the Invention
The present invention relates to a method of manufacturing mirror-polished silicon wafers in which processes such as formation of a gettering region, formation of a dopant-volatilization-prevention film, and heat treatment for anihilation of oxygen donors are performed successively and selectively. The present invention also relates to an apparatus for processing silicon wafers in which processes such as formation of a gettering region, formation of a dopant-volatilization-prevention film, and heat treatment for anihilation of oxygen donors are performed successively and selectively.
2. Description of the Related Art
As shown in FIG. 1, mirror-polished silicon wafers used for manufacture of silicon devices are generally manufactured through a slicing process A for slicing a silicon monocrystalline rod manufactured by a silicon monocrystal manufacturing apparatus; a chamfering process B for chamfering the peripheral edge of each of the silicon wafers thus sliced in the slicing process A in order to prevent the silicon wafer from becoming cracked or chipped; a lapping process C for lapping the thus-chamfered silicon wafer so as to form a flat surface thereon; an etching process D for eliminating mechanical damage remaining in the chamfered and lapped silicon wafer; a mirror-polishing process E for polishing at least one main face of the etched silicon wafer; and a cleaning process F for cleaning the mirror-polished silicon wafer so as to remove polishing agent and foreign matter adhered thereto.
In most cases, the mirror-polishing process E is not performed immediately after the etching process D, but, as shown in FIG. 1, an additional process G is performed between the etching process D and the mirror-polishing process E. Depending on the specifications (or application) of mirror-polished silicon wafers to be manufactured, there is carried out, as the additional process G, heat treatment for anihilation of oxygen donors, or formation of a dopant-volatilization-prevention film or a gettering region (gettering film or gettering damaged layer) on a face (hereinafter referred to as a "back surface") opposite the main face (hereinafter referred to as a "front surface") on which devices will be fabricated. In the example shown in FIG. 1, after silicon wafers undergo the etching process D, a % of the silicon wafers are transported to a process for formation of a dopant-volatilization-prevention film, b % of the silicon wafers are transported to a process for heat treatment for anihilation of oxygen donors, c % of the silicon wafers are transported to a process for formation of a gettering film, and d % of the silicon wafers are transported to a process for formation of a gettering damaged layer. The sum of a, b, c, and d is approximately 100%. Subsequently, x % of the silicon wafers that have undergone the heat treatment for donor anihilation are transported to the process for formation of a dopant-volatilization-prevention film, y % of the heat-treated silicon wafers are transported to the process for formation of a gettering film, and z % of the heat-treated silicon wafers are transported to the process for formation of a gettering damaged layer.
Since the additional processes are conducted at different apparatuses, when the silicon wafers must undergo two or more additional processes, they must be transported from one apparatus to the next apparatus. During such transportation, foreign matters may adhere to the silicon wafers. Therefore, the silicon wafers that have undergone an additional certain process must be cleaned before being subjected to the next additional process. Moreover, since the respective additional processes have different processing performances (throughputs), there is a waiting period before wafers can undergo the next process, resulting in a stock of wafers being formed between processes (hereinafter referred to as "process stock"). Therefore, when two or more kinds of additional processes are performed, the productivity decreases, resulting in an increased cost of mirror-polished silicon wafers. Also, delivery becomes delayed.
Moreover, in recent years, mirror-polished silicon wafers have been required to have various kinds of additional functions such as a gettering function. With this trend, the specifications of mirror-polished silicon wafers to be manufactured have become diversified. Since the number, kinds and sequence of required additional processes depend on a desired additional function and therefore a process stock is generated, the diversification of specifications has also caused an increase in the process stock and a decrease in productivity.
Also, when apparatuses for carrying out the respective additional processes are installed at different sites or in different buildings, silicon wafers must be transported over a long distance between the apparatuses, so that the productivity decreases further.